Clutches

ABSTRACT

A dual clutch transmission has a driving plate defining concentric engagement surfaces, concentric friction plates, concentric pressure plates, and first and second clutch springs for operation of the pressure plates in clamping the friction plates against their respective engagement surface on the driving plate. The driving plate has a top hat type configuration, whereby the engagement surfaces are axially off set from one another. Cooling passages may be provided in the driving plate. The dct is preferably nested, wherein the outer pressure plate is in axial alignment with the radially inner portion of the driving plate, the inner pressure plate is in axial alignment with the radially outer portion of the driving plate, and the friction plates are arranged in axial alignment with one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 12/445,311 filedon Jul. 16, 2009. Application PCT/GB2007/003894 claims priority forApplication 0620347.5 filed on Oct. 13, 2006 in the United Kingdom.Application PCT/GB2007/003894 claims priority for Application 0709409.7filed on May 16, 2007 in the United Kingdom. ApplicationPCT/GB2007/003894 claims priority for Application 0712091.8 filed onJun. 22, 2007 in the United Kingdom.

FIELD OF THE INVENTION

The present invention relates to clutches, and more particularly, butnot exclusively, to clutches for automotive applications, such as dualclutch transmissions.

BACKGROUND OF THE INVENTION

The performance of a friction clutch deteriorates with an increase inclutch plate temperature. For this reason, ‘wet clutches’ are known inwhich the clutch components are contacted by lubricating fluid to reducefriction and transfer heat.

Wet clutches are commonly used in automotive applications, such as indual clutch transmissions. However, wet clutch assemblies generallyintroduce inefficiencies, such as through churning losses caused by dragbetween the lubricating oil and moving components within the assembly.Hence, there is a need to provide clutch cooling with reducedinefficiency.

Dual clutch transmissions typically include a pair of clutches, eachhaving a driving plate and a pressure plate, for clamping a frictionplate therebetween. There is a need to optimise the packaging and weightof such transmissions.

SUMMARY OF THE INVENTION

An object of the invention is to provide alternative means for coolingclutch plates. Another object of the invention is to provide an improveddual clutch transmission, more particularly, but not exclusively, animproved driving plate for a dual clutch transmission.

According to one aspect of the present invention, there is provided adriving plate for a clutch assembly, the driving plate having one ormore internal passageways, ducts, chambers, or bores for receiving athermal transfer medium.

The transfer medium is preferably a coolant fluid. The heat transfermedium may take the form of a heat tube, preferably of knownconstruction (e.g. linear or rotary), or a conductive core, e.g. acopper core fitted within a bore in the driving plate.

Such arrangements can be used to reduce the temperature of a dry clutchassembly, to the extent that it may be possible to use a dry clutchassembly where previously a wet clutch assembly was deemed necessary,e.g. in a dual clutch transmission. The above arrangements are alsosuitable for use in wet clutch applications and other types of clutchassembly, e.g. wherein the driving plate is in the form of a flywheel.Hence, the term driving plate should be understood to mean a plate ordriving member within a clutch against which a friction plate isintended to be clamped in use.

Preferably the driving plate includes a coolant circuit for receiving aflow of cooling fluid. The circuit may include one or more passagewaysextending within the plate. It may be preferred to locate the inlet andoutlet of the circuit at a radially inner region of the plate, e.g. inor adjacent the central bore of an annular driving plate (whether in anaxial end face of the plate or in a radial portion of the plate).

In preferred embodiments, the driving plate has opposing engagementsurfaces, e.g. for use with opposing pressure plates in a dual clutchtransmission. In such embodiments, it is preferred if the driving plateis cranked, so as to define a pair of parallel offset portions, eachhaving an engagement surface. Said offset portions are preferablyconnected via an angled or transverse intermediate portion. This canreduce the overall length of the clutch assembly for a dual clutchtransmission.

According to another aspect of the invention, there is provided a clutchassembly, preferably a dry clutch assembly, including a driving plateaccording to any of the above aspects of the invention. The clutchassembly is preferably part of a dual clutch transmission.

Such clutch assemblies are advantageous in that the driving plate iscooled in use and can be used to cool a friction plate within theclutch, via thermal transfer between the driving plate and the frictionplate, e.g. when the two plates are engaged.

In a preferred embodiment, the clutch assembly is part of a dual clutchtransmission having concentric input shafts, wherein the circuit has aninlet and an outlet which are arranged in communication with the innerof said input shafts. In another embodiment, the inlet and outlet arearranged in communication with the outer of said input shafts.

In each case, a sleeve or insert may be provided within thecommunicating input shaft, for separating the cylindrical volume of theshaft, so as to define inlet and outlet pathways for fluid in saidcircuit.

In a preferred embodiment, the circuit has an inlet arranged incommunication with the inner input shaft and an outlet arranged incommunication with the outer input shaft.

The circuit preferably includes means for promoting the flow of coolantfluid through the driving plate, such as spiral, auger type projections.The flow promoting means are preferably formed in the transmission inputshafts, and may take the form of integrally machined formations.Additionally or alternatively, the formations may form part of thesleeve/insert. The sleeve/insert may be rotatable with the shaft, but ispreferably fixed against rotation, for promoting fluid transfer.

Conveniently, the circuit may be arranged in communication with theengine cooling circuit of a vehicle.

The coolant fluid may be taken directly from the engine cooling circuit.Alternatively, there may be a separate circuit, e.g. containing water oranother coolant fluid, which communicates with the engine coolingcircuit via a heat exchanger. In either case, the coolant fluid may bedirected to a heat rejection device on exiting the driving plate.

In order to deal with packaging constraints at the engine side of theclutch (and indeed to avoid the need for significant modifications tothe engine), it is preferred if the circuit includes a conduit whichdirects a flow of coolant fluid away from the engine to the transmissionside of the clutch. The coolant may then be supplied to the drivingplate along a passageway inside one of the transmission input shafts,for example.

The driving member is preferably supported on one or more bearings, e.g.a bearing located on the inner or outer input shafts of a dual clutchtransmission.

Flow control means, for example one or more controlled valves or athermostatic control, may be provided for controlling the flow ofcooling fluid to or from the plate.

According to a further aspect of the invention, there is provided aclutch assembly, preferably a dry clutch assembly, having a drivingplate which is arranged in communication with a thermal transfer mediumfor use in cooling the driving plate.

The thermal transfer medium is preferably arranged to communicate with anon-engagement surface of the driving plate, i.e. a portion of the platewhich is not intended for use in engaging another plate within theclutch, and so the thermal transfer medium is distinct from a gas (e.g.air) or a liquid (e.g. lubricating oil) which is specifically intendedto come into contact with the engagement surface of a driving plate suchas a flywheel so as to cool said surface.

Preferably, the thermal transfer medium is arranged for communicationwith the driving plate at a radially inner region of the driving plate,e.g. at or adjacent the internal bore of annular driving plate.

The thermal transfer medium may include one or more conductive elementsmounted on or in contact with driving plate, e.g. to allow for heattransfer between the driving plate and an externally cooled component.Additionally or alternatively, the thermal transfer medium may take theform of or include a conductive powder and/or a conductive fluid incontact between the driving plate and an externally cooled component.

In a preferred embodiment, the clutch assembly is part of a dual clutchtransmission and the externally cooled component is in the form of aninput shaft of said transmission which may be cooled via a flow ofcooling fluid adjacent or within the shaft or via an oil bath at alocation remote from the clutch. The thermal transfer medium may bearranged between the shaft and the driving plate for thermal transferbetween the shaft and driving plate.

It may be preferred to isolate the thermal transfer medium in acartridge that can be arranged in communication with the driving plateand the externally cooled component. One or more walls of the cartridgeare preferably of a conductive material, e.g. a metal such as copper.

In preferred embodiments, the driving plate has opposing engagementsurfaces, e.g. for use with opposing pressure plates in a dual clutchtransmission. In such embodiments, it is preferred if the driving plateis cranked, so as to define a pair of parallel offset portions, eachhaving an engagement surface. Said offset portions are preferablyconnected via an angled or transverse intermediate portion.

In each of the above aspects of the invention, cooling of the drivingplate can improve the functionality of the clutch assembly bystabilising the frictional characteristics, thereby affording bettercontrol and improved shift quality. It can also be useful in reducingthe cost of the friction materials of the clutch, whereby a lowerspecification of friction facing can be employed than would otherwise berequired. It may also be of assistance in reducing the size and mass orinertia required for a given application.

According to another aspect of the invention, there is provided a clutchassembly having a driving plate coupled to a pressure plate by aconductive element for the thermal transfer between the driving plateand the pressure plate.

Conveniently, the conductive element may be fixedly secured to thedriving plate and/or the pressure plate.

The conductive element may take the form of a metallic element, such asa strip of sprung copper or copper foil. In a preferred embodiment, theconductive element is in the form of a flexible copper braid, which ispreferably pinned or otherwise fastened to either plate. In anotherembodiment, the conductive element is in the form of a copper bellows.

Conveniently, the conductive element may be of generally annular form.One or more additional conductive elements may be incorporated forthermal transfer between the driving plate and pressure plate.

It is most preferred if the driving plate is subject to cooling, e.g.having one or more internal chambers for receiving a cooling fluid,and/or wherein the driving plate is arranged in communication with aconductive powder and/or a conductive fluid and/or conductive brushes,preferably as part of a dry clutch assembly.

In the above embodiments, thermal transfer is able to take place betweenthe cooling medium and the driving plate, so as to cool the drivingplate. Further thermal transfer takes place between the driving plateand the or each pressure plate, via the or each conductive element.

In preferred embodiments, the driving plate has opposing engagementsurfaces, e.g. for use with opposing pressure plates in a dual clutchtransmission. In such embodiments, it is preferred if the driving plateis cranked, so as to define a pair of parallel offset portions, eachhaving an engagement surface. Said offset portions are preferablyconnected via an angled or transverse intermediate portion.

According to still further aspect of the invention, there is provided adual plane driving plate having opposing engagement surfaces, e.g. foruse with opposing pressure plates in a dual clutch transmission.

Such an arrangement is advantageous in that it can reduce the length ofa clutch assembly.

In such embodiments, it is preferred if the driving plate is cranked, soas to define a pair of parallel offset portions, each having anengagement surface. Said offset portions are preferably connected via anangled or transverse intermediate portion.

According to yet a further aspect of the invention, there is provided adual clutch transmission including a single driving plate having firstand second engagement surfaces for engagement with first and secondfriction plates.

The driving plate is preferably cranked, so as to define a pair ofparallel offset portions, each having an engagement surface. Said offsetportions are preferably connected via an angled or transverseintermediate portion. In other embodiments, the engagement surfaces arenot parallel with one another. For example, the first engagement surfacemay be configured for extending in a generally radial direction in use,e.g. perpendicular to the axis of rotation, whereas the secondengagement is arranged at and angle, forward or rearward, to said firstengagement surface, e.g. anywhere between at 5 and 90 degrees relativeto the first engagement surface. In one embodiment, the first engagementsurface is perpendicular to the second engagement surface. In otherembodiments, the second engagement surface is arranged at 15, 30, 45,60, or 75 degrees relative to the first engagement surface.

In a preferred embodiment, the transmission includes a driving platedefining concentric engagement surfaces, concentric friction plates,concentric pressure plates, and first and second clutch springs foroperation of the pressure plates in clamping the friction plates againsttheir respective engagement surface on the driving plate.

Preferably, the driving plate has a top hat type configuration, wherebythe engagement surfaces are axially off set from one another.

Preferably, the outer pressure plate is in axial alignment with theradially inner portion of the driving plate, and the inner pressureplate is in axial alignment with the radially outer portion of thediving plate. Preferably, the friction plates are arranged in axialalignment with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and features of the invention will be readily apparentfrom the claims and the following description of preferred embodiments,made by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic cross sectional view through a dry clutchassembly,

FIG. 2 is similar to FIG. 1, showing a modified dry clutch assembly;

FIG. 2A is a schematic view of a bellows for use in the clutch assemblyof FIG. 2;

FIG. 3 is similar to FIGS. 1 and 2 and shows an alternative dry clutchassembly;

FIG. 3A is a schematic view of a modified driving plate including aconductive brush;

FIG. 4 is a schematic view of a heat transfer cartridge for use in theassembly of FIG. 3;

FIG. 5 is similar to FIG. 3 and shows a further dry clutch assembly witha conductive core;

FIG. 6 is a schematic cross-section through of a nested dry DCTarrangement; and

FIG. 7 is an exploded view of the DCT arrangement from FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A liquid-cooled dry clutch assembly is indicated generally at 100 inFIG. 1, which includes a driving plate 102 having a series of internalbores or passageways. More particularly, the illustrated plate 102 hastwo parallel and radially extending passageways 104, 106 connected toone another by a relatively short transverse passageway 108. Thepassageways 104, 106 form part of a circuit for directing a flow ofcooling fluid into and out of the driving plate 102 at a radially innerportion of the plate 102.

In this embodiment, the clutch assembly 100 is part of a dual clutchtransmission (DCT), having concentric input shafts 110, 112. The drivingplate 102 is supported on a bearing 114 located on the inner shaft 110,although it could be supported on the outer shaft 112.

To reduce the axial length of the assembly, the driving plate 102 iscranked so as to define two parallel and offset portions 116, 118connected to one another via a transition portion 120. Each offsetportion 116, 118 has an engagement surface arranged to cooperate with arespective pressure plate 122 for clamping a respective friction plate130, 132 of the DCT. The friction plates 130, 132 are splined onto theirrespective shaft 110, 112.

In this embodiment, the cooling circuit only extends into the radiallyinner offset portion 116, although in other embodiments it may extendinto both portions 116, 118, e.g. substantially along the entire radialdimension of the plate 102.

As illustrated, the cooling circuit has an inlet 124 and an outlet 126arranged in communication with the inner shaft 108 of the DCT. A sleeve128 is provided within the shaft 110 for separating the cylindricalvolume of the shaft 110, so as to define inlet and outlet flow paths forthe cooling fluid. The arrows in FIG. 1 denote the direction of coolantflow for this embodiment.

In this embodiment, the coolant fluid is taken directly from the enginecooling circuit. Flow control means, for example one or more valves or athermostatic controls (not shown) may be provided for controlling theflow of cooling fluid to or from the plate 102.

In use, a flow of coolant fluid is provided through the passageways 104,106, 108 in order to cool the plate 102. Thermal transfer occurs withinthe plate 102 leading to a cooling of the external surface of the plate102. Thermal transfer also occurs across the engaged plates during use.The flow of coolant through the circuit can be continuous or selectivelycontrolled, for example to ensure that there is sufficient flow orcooling under specific vehicle driving conditions, e.g. under heavy loadconditions.

In a most simple embodiment (not illustrated) the driving plate includesa single fluid receiving chamber, preferably extending in a generallyradial direction, and more preferably to a radial outer region of theplate.

The cooling chamber/circuits referred to above may be incorporated inthe driving plates of wet or dry clutch assemblies, including in ‘singleplane’ driving plates.

Referring now to FIG. 2, a further dry clutch assembly is indicated at200. The assembly 200 is similar in many ways to the assembly 100described above and so it will not be described in detail. Commonfeatures are given the same reference numerals, albeit with a prefix 2—.

A conductive element 250, which in his embodiment is in the form of anannular metallic braid, is arranged in communication between the drivingplate 202 and the pressure plates 222. In particular, the braid isfastened to the respective plates by pins 252, so as to be fixed forrotation with the driving plate 202 and pressure plates 222.

In addition to any heat exchange across the engaging surfaces of thedriving plate in use, thermal transfer is effected between the drivingplate 202 and the pressure plates 222 via the conductive element 250.Hence, as the driving plate 202 is cooled internally by the coolantcircuit, a cooling effect is experienced by the pressure plates 22, viathe braid 250.

In the drawings, the conductive element 250 is shown in abutment withthe steel member 254 by means of which the sprung steel torque straps256 are connected to the outer pressure plate 222. However, it ispreferred if a spacing exists between the steel 254 and the conductiveelement 250.

It may be preferred if the torque straps 256 are made from a highlyconductive material such as brillium copper, rather than conventionalsprung steel. Indeed, by using highly conductive torque straps 256, itis possible to obviate the need for the conductive element 250, wherebythermal transfer occurs between the driving plate 202 and the pressureplates 222, via the torque straps 256 and steel 254. The applicantreserves the right to claim independent protection for this feature.

One or more additional conductive elements may be incorporated. It maybe preferred to have a dedicated conductive element associated with eachpressure plate in addition to or as an alternative to one common elementfor both pressure plates.

In certain embodiments, the conductive element may take the form of abellows, e.g. of copper. An example is shown at 260 in FIG. 2A, thebellows 260 having convolutions 262.

Referring now to FIG. 3, a modified dry clutch assembly is indicated at300. The assembly 300 is similar in many ways to the assemblies 100, 200described above and so it will not be described in detail. Commonfeatures are given the same reference numerals, albeit with a prefix 3—.

Cooling of the driving plate 302 is effected by a cooling medium(indicated generally at 370) which is arranged in communication with aradially inner portion of the driving plate 302 and a separate cooledpart of the clutch assembly 300. A seal 374 is provided on either sideof the void for the cooled medium 370.

In this embodiment, the radially inner surface is in actual fact acylindrical face 372 of the driving plate 302. Moreover, the coolingmedium 370 is arranged between said face 372 and a portion of the innershaft 310 of the dual clutch transmission. The inner shaft 310 issubject to cooling, e.g. from oil at a location remote from the plates302, 322, or via a flow of cooling fluid adjacent to or within the shaft310 (e.g. in a manner similar to FIG. 1).

The cooling medium 370 may take the form of conductive brushes (solid orflexible), e.g. connected to the driving plate 302 and/or the shaft 310,whereby thermal transfer between the shaft 310 to the driving plate 302,via the brushes, can serve to cool the driving plate 302.

FIG. 3A shows a modified driving plate 302 of cranked configuration,which incorporates block 358 of conductive material such as coppermounted on a spring 357, wherein the block is configured to brushagainst an externally cooled component, for example inner shaft 310,against the action of the spring 357, in order to cool the driving plate302. Multiple brushes can be provided in radial tracks within the springvoid. Thermally conductive paste is preferably used between thosesurfaces intended to transfer heat.

In preferred embodiments, the cooling medium may be in the form of aconductive powder and/or fluid which is held in a sealed manner betweenthe driving plate 302 and the shaft 310. FIG. 4 shows a cartridge 400consisting of inner and outer shells 402, 404 which are configured forco-rotation with their respective mating parts 302, 310. The shells 402,404 are made from copper, so as to facilitate thermal transfer betweenthe drive plate 302, cooling medium 370 and shaft 310. Again, athermally conductive paste can be applied between mating surfaces tofurther enhance thermal transfer.

The seals 374 are compressed between the shells 402, 404 so as tomaintain a positive pressure in the conductive medium 370, so as tomaintain a high degree of ‘wetting’ contact with the respective innersurfaces of the shells 402, 404.

Although a conductive element 350, 550 is shown between the pressureplates 322, 522 and the driving plate 302, 502 in FIGS. 3 and 5, it ismaybe omitted, if preferred.

Referring now to FIG. 5, a modified dry clutch assembly is indicated at500. The assembly 500 is similar in many ways to the assemblies 100,200, 300 described above and so it will not be described in detail.Common features are given the same reference numerals, albeit with aprefix 5—.

In this embodiment, the driving plate 502 includes an internal conduit595, which can be used to contain a thermal transfer medium, such as acast copper core, for cooling the driving plate 502 via the thermaltransfer medium 570 between the driving plate 502 and the externallycooled component. This can be used in combination with other coolingfeatures of the kind described herein, if desired. Indeed, anycombination of the conductive or cooling features shown or described inrelation to FIGS. 1 to 5 can be used, as required.

Referring now to FIGS. 6 and 7, a nested DCT assembly is indicatedgenerally at 600.

The assembly 600 includes a driving plate 602 defining concentricengagement surfaces 604, 606, concentric friction plates 608, 610,concentric pressure plates 612, 614. The assembly 600 further includesfirst and second clutch springs 616, 618 for operation of the pressureplates 612, 614 in clamping the friction plates 608, 610 against theirrespective engagement surfaces 604, 606 on the driving plate 602. Theabove components are mounted in a housing 620.

The driving plate 602 has a top hat type configuration, whereby theengagement surfaces 604, 606 are axially off set from one another. Inthis embodiment, the outer pressure plate 614 is in axial alignment withthe radially inner portion of the driving plate 602, and the innerpressure plate 612 is in axial alignment with the radially outer portionof the driving plate 602. Moreover, the friction plates 608, 610 are inaxial alignment with one another. The outer pressure plate 614 has a tophat configuration, whereas the inner pressure plate 612 is generallyplanar.

Specific operation of the clutch will be understood by the skilledaddressee and is not described herein.

It should be noted that the assemblies 100, 200, 300, 500, 600 areconfigured to be open under normal operating conditions, wherebypressure has to be applied to engage the clutch.

Although the illustrated embodiments relate to clutch assemblies fordual clutch transmissions, it will be understood that many of theprinciples described herein are equally applicable to single plateclutch assemblies and single clutch transmissions, whether normally openor normally closed, and other types of wet or dry clutch assembly.

The cooling arrangements described and illustrated herein are applicableto any driving plate for a clutch, whether cranked, planar or otherwiseconfigured.

1. A clutch assembly having a driving plate arranged in communicationwith a thermal transfer medium for use in cooling the driving plate,wherein the thermal transfer medium is at least one conductive brusharranged between the driving plate and a separate cooled part of theclutch assembly for cooling the driving plate.
 2. A clutch assemblyaccording to claim 1 wherein said at least one conductive brush ismounted with the driving plate and is arranged to brush against saidcooled part of the clutch assembly.
 3. A clutch assembly according toclaim 2 wherein the brush is resiliently biased for contact with saidcooled part of the clutch assembly.
 4. A clutch assembly according toclaim 2 wherein the brush is mounted in a recess on the driving plate.5. A clutch assembly according to claim 1 wherein the brush projectsfrom a cylindrical surface of the driving plate for contact with aseparate part of the clutch assembly.
 6. A clutch assembly according toclaim 1 wherein the driving plate includes a recess, with multipleconductive brushes mounted in said recess and biased for contact with anexternally cooled part of the clutch assembly for cooling the drivingplate.
 7. A clutch assembly according to claim 1 wherein the thermaltransfer medium is arranged to communicate with a non-engagement surfaceof the driving plate.
 8. A clutch assembly according to claim 1 whereinthe thermal transfer medium is arranged for communication with thedriving plate at a radially inner region of the driving plate.
 9. Aclutch assembly according to claim 1 wherein the thermal transfer mediumincludes one or more conductive elements mounted on or in contact withthe driving plate configured to allow for heat transfer between thedriving plate and an externally cooled component of the clutch assembly.10. A clutch assembly according to claim 1 wherein the thermal transfermedium is in the form of a conductive powder and/or fluid which is heldin a sealed manner between the driving plate and a separate part of theclutch assembly and arranged for thermal transfer between the drivingplate and said separate part of the clutch assembly.
 11. A clutchassembly according to claim 10 wherein the thermal transfer medium isheld in a conductive cartridge between the driving plate and theseparate part of the clutch assembly.
 12. A clutch assembly according toclaim 1 wherein the driving plate has a chamber for receiving a coolantfluid.
 13. A clutch assembly according to claim 12 wherein the chamberforms part of a circuit for directing a flow of cooling fluid into andout of the plate.
 14. A clutch assembly according to claim 13 whereinthe plate is annular and defines a cylindrical face, wherein an inletand an outlet for the passage of coolant fluid is formed at or adjacentsaid face.
 15. A clutch assembly according to claim 1 wherein thedriving plate is coupled to a pressure plate by a conductive element forthe thermal transfer between the driving plate and the pressure plate.